In an earth-moving machine or vehicle, such as an excavator or a loader, brakes perform important functions. Brakes are used for power management in a vehicle, including an electric drive vehicle. Typically, an electric drive vehicle has an electric motor that propels the vehicle and a brake that slows down the vehicle. By engaging the brake, the vehicle can slow down quickly, for example, to avoid an obstacle or change its moving direction. Thus, earth-moving vehicles need a brake for safety as well as their operating efficiency.
Under certain operating conditions, the vehicle is operated in a retarding or regenerating mode. Typically, retardation or regeneration occurs when the vehicle slows down from its present speed or the vehicle is pulled due to the gravity. The vehicle may experience the retarding mode, for example, when it goes down a steep hill. In such instances, the vehicle needs to dissipate energy to slow down or maintain its speed. If the vehicle does not dissipate or absorb energy when going down a steep slope, then the vehicle simply accelerate to faster and faster speeds. Similarly, the vehicle needs to dissipate or absorb energy to slow down.
In the retarding mode, the brake is often used to dissipate extra energy or power for better vehicle performance and safety. While a brake is an important part of any earth-moving vehicle, it should not unnecessarily interfere with the vehicle performance. For example, the brake control should not interfere with a motor speed control before the motor power limitation is reached. Also, brake control should provide stability to the operation of the vehicle.
Some attempts have been made to provide such braking control. For example, U.S. Pat. No. 6,551,212 discloses a decelerator system for a work machine. The deceleration system has a machine control device including an engine control, a transmission control, and a brake control. The machine control device receives an engine control signal, a transmission control signal, and a brake control signal. While the decelerator system disclosed in U.S. Pat. No. 6,551,212 provides a good system to decelerate a vehicle, a brake control system that provides automatic, integrated control of the motor and brake is desired. It is further desirable to provide an automatic brake control system that has more robust stability and does not sacrifice vehicle performance. It is also desirable to provide an integrated motor/brake control system that can handle system uncertainties with excellent stabilities.
Thus, the present brake control system is directed to solving one or more of the shortcomings associated with prior art designs and providing a braking control system with more stability and less interference with the vehicle performance.